Devices for detecting the proximity of a police vehicle to a moving vehicle are well-known. Such devices are normally utilized by the vehicle operator to maintain his speed within the posted speed limit when a police vehicle is in the vicinity. Usually, police vehicles are detected by detecting transmissions of the police radar system.
Another approach is to detect voice radio transmissions by the police vehicle. Generally, this technique is not practical since the power of such radio transmissions is so great that they are picked up by a detector over a very wide area. Recently, however, many police agencies are utilizing a system known as a mobile extender to provide the capability for police officers to communicate with the dispatcher and with other police vehicles by means of a handheld radio or walkie-talkie when they are outside the police vehicle. In the mobile extender system, the police vehicle is equipped with a low power transceiver for communicating with the handheld radio at one frequency. Transmissions between the vehicle and the dispatcher are carried on a high power transmitter at a different frequency. The mobile extender transceiver has a range of approximately 3-4 miles and transmits when the police dispatcher is communicating with that police vehicle or any other police vehicle within the district. Accordingly, transmissions by the mobile extender transceiver are frequent.
It is a general object of the present invention to provide apparatus for detecting transmissions of a radio transmitter of known frequency and power within a predetermined distance from a moving vehicle.
It is another object of the present invention to provide apparatus for detecting the proximity of a police vehicle to a moving vehicle by detecting voice radio transmissions by the police vehicle.
It is another object of the present invention to provide apparatus for detecting the proximity of a police vehicle to a moving vehicle wherein an operator alarm remains active until the moving vehicle has passed the police vehicle.
It is another object of the present invention to provide police vehicle detection apparatus which is reliable and low in cost.